Method for making a three-dimensional body

ABSTRACT

The present invention relates to a method for making a three-dimensional body, the construction of which is realised in layers by a purposeful application of material. According to the invention, two different materials are applied to each layer. One is purposeful applied in line along the outer edge of the three-dimensional object in the corresponding section plane, the remaining surfaces being filled with the second material.

BACKGROUND OF INVENTION

1. Field of Invention

The invention is based on a method for making a three-dimensional bodyfrom a computer data model by computer-controlled layer-wise depositionof material.

2. Description of Related Art

The continued intensification of international competition withever-decreasing product cycles calls for reduction of development time.Rapid production of prototype models yields a great cost reductionpotential during all design and development phases,

Existing methods for computer controlled manufacturing ofthree-dimensional objects can be categorised into subtractive andadditive methods. The most popular method of the first group isnumerically controlled milling. Disadvantages result from geometricalrestrictions even with up to five axes milling. This method isinherently expensive, especially for single pieces, and requiressuitable equipment together with a trained operator.

The second group comprises newer methods like e.g. stereolithography.Here a container with liquid photopolymer resin with constant fluidlevel is equipped with a mechanical fixture, which allows for loweringof a submerged platform according to a desired layer thickness. In afirst step, a resin film of exact thickness is being applied on thesubmerged platform by a wiper (doctor blade). In a subsequent step, theresin film is being cured in selected areas by radiation from a UVlaser. Hereby the laser beam scans across the resin surface undercomputer control, exposing contour lines, solid areas, and supportingstructures to UV radiation. The next step comprises lowering theplatform in the resin container by one layer thickness, applying anotherresin layer, and repeating the radiation exposure for the desiredgeometry of this layer. This cycle is repeated until completion of theobject. Finally the model is being removed from the resin bath, cleanedfrom residual uncured resin, and separated from the supportingstructures.

This method is primarily limited by its high expenses for equipment,process, and consumables. Additional equipment for cleaning of themodels from liquid resin is mandatory.

EP-A-0 322 257 discloses a similar method in which a photosensitivematerial is being exposed to radiation through a computer generated maskin a layer-wise fashion. Subsequently unexposed material is beingremoved and substituted by an non-photosensitive material. The processis repeated layer by layer until completion of the model.

This method requires expensive cleaning equipment for removal ofunwanted material during each layer cycle, yielding a large amount ofstill reactive waste,

This disadvantage is avoided by methods like selective laser sintering,disclosed in U.S. Pat. No. 4,247,508. Here a thin powder layer is beingapplied to the building platform and selectively melted by a computercontrolled scanning laser beam. Again, the cycle is repeated untilcompletion of the model. Plastic or metal powders can be used. Ifdesigned skilfully, the loose powder can serve as supporting means.Therefore blowing off of unmelted powder after completion of thebuilding phase is sufficient in order to get the finished model.

But this method requires expensive lasers, optics, and scanning devicesas well. Furthermore, a certain degree of surface roughness of themodels is caused by the granularity of the powder (ca. 50-100micrometers average grain diameter).

A similar method, developed by the Massachusetts Institute of Technologyand disclosed in EP 0 431 924 B1, applies thin powder layers on asubstrate in which powder particles are bonded together according to thedesired model cross-section by selectively adding small glue dropletsvia a printhead. The building material consists of bonded powderparticles; unbonded powder acts as support and is being removed aftercompletion of the process.

This method is used predominantly for building moulds for investmentcasting together with ceramics and has some disadvantages caused by thecomplex powder handling procedures. Moreover, the models always consistof a powder-binder composite which never achieves the bulk materialdensity and therefore is mechanically weak,

In “Ballistic Particle Manufacturing” of the BPM company molten materialis being deposited from a single nozzle which is being positioned by afive-axis unit. Supporting structures can be omitted. The method istime-consuming, because only one nozzle is used for material deposition.To save time, only hollow bodies are being made today. Anotherdisadvantage results from uneven material distribution, which leads to adeeply grooved object surface.

WO 95/05943 is based on dosing two different materials via dropgenerators, where the first material generates a model cross-section,the second a support structure where needed. Upon completion of thebuilding phase the support structure is being removed by submersion in asolvent. This step yields the finished model which consists of insolublematerial.

This technique has its advantages when building subtle structures, butthe process is very slow because of the two dosing steps, leading tounacceptable building times. Moreover, material properties are verylimited by the current maximum temperature of 80 degrees Celsius in thedosing head.

In EP 0 500 225 B1 a method is disclosed which also uses two differentmaterials. The first material is used for building the model byselective dosing with a dosing head. The second material, whoseapplication method is not specified, yields a support structure.

Here, too, the disadvantage holds that the building material must becompatible with the dosing heads, reducing the choice of materials andquality. The dosing process is technically demanding, because thebuilding material must be pre-heated. Large models are enormously timeconsuming for the large amount of selectively deposited material.

SUMMARY OF THE INVENTION

Considering the problems described above which are associated withcurrent methods, it is the objective of the invention to create a methodfor rapidly making three-dimensional objects with low technical effortwhich is suited for operation in an office environment.

This objective is achieved by a method for making a three-dimensionalbody comprising the properties laid down in the first claim.

According to the present invention a three-dimensional body can be madein the following steps:

a) Applying a release agent in its liquid state onto selected areas of abuilding platform by a single-drop generator, using a pattern accordingto the cross-section of a thin-walled shell around the three-dimensionalbody, and a grid pattern across the remaining area of the buildingplatform.

b) after completion of the pattern for the current layer, filling of theareas enclosed by the release agent with a curable resin.

c) Curing of the resin.

d) Smoothing and planing of the layer in order to expose the uppersurface of the release agent.

e) Repeating of the steps a) to d) with patterns according to thecurrent cross-section of the three-dimensional body, thereby making thebody itself.

f) Removing the structures not belonging to the body by dissolving therelease agent.

The method according to this invention can be realised by a device formaking three-dimensional bodies directly from computer data whichconsists of:

A microcomputer for data processing and control of the building process,

a building platform which can be moved vertically in a stepwise fashion,

a dosing device for selective application of the release agent,comprising positioning actuators, which can be moved across the buildingplatform under computer control so that release agent can be applied atany point,

a dosing device for uniform and rapid application of resin across theentire building platform,

a device for curing of the resin and

a device for smoothing and planing of the completed layer made up ofrelease agent plus resin.

The advantage of the present invention in comparison with the state ofthe art consists of the combination of a selective material deposition,mostly in lines and a non selective, rapid application of resin forfilling up the layer. Due to the application of the release agent insmall regions during the first step the whole process will beaccelerated significantly.

Moreover, the differentiation between building and support material canbe neglected because both structures will be formed by the same materialduring the rapid application of the resin. The differentiation is madedue to the location of the material, either it is located inside theregion enclosed by the border corresponding to the section plane of theobject and therefore building material, or outside the border andtherefore support material. The applied release agent is the prepositionfor this decision. Therewith the process is significantly faster thanall the processes described above.

The building of a cavity is possible by filling the release agentlayerwise in regions which belong to the cavity volume. By solving therelease agent after the process, extracting the object and emptying thecavity through a provided hole the designated object will be demoulded.

Due to the use of a inkjet like drop-on-demand dosing device for theapplication of the release agent, cost-effective and accurate systemscan be designed which will reduce the overall system price.

Additionally the choice of different building materials is much widerthan with the processes described above, because material propertieslike viscosity and surface tension in the liquid state are affecting theapplication much less. Due to that, objects with much better propertieslike rigidity, stiffness, hardness and surface quality can be made.

Because of the wide choice of materials, it is possible to find materialcombinations which will produce less emissions during the buildingprocess and which are not affective to skin. Due to that, the mostimportant requirement for an office compatible device is fulfilled.

After the process the complete building volume is taken from the deviceas a solid cube. Therefore no special handling devices are necessary.There is no loose particle material or unhardened resin which canpollute the environment or affect the user.

With a suitable composition of a release agent the removal of thenon-object-parts can be done without any tools. According to the presentinvention solving of the release agent is possible by a solvent,preferably water or by means of heat.

Due to the complete hardening of the resin there is no hazardous waste.

By means of the present invention any object geometry can be produced inshort time and without use of other means, provided that object definingthree-dimensional computer data exist, for example CAD-data, Other datasources can be used as well, for example data out of three-dimensionalscanners.

The data of the desired object will be transferred to the controlcomputer which adds a thin-walled, closed shell to, the object geometry.Subsequently the shell will be sliced perpendicular to the building axesaccording to the current progress. To facilitate demoulding of theobject after the process a thin-walled grid structure will be added tothe present slice data covering the whole building area. These geometrydata will be plotted onto the building platform using the release agent.Preferably the release agent will be applied by means of a computercontrolled droplet generator similar to drop-on-demand ink-jet printers.For that a dosing head with one or more nozzles will be fitted to a pairof axes which are perpendicularly movable to each other and are capableof positioning the droplet generator to any point of the building area.The liquid release agent in the heated dosing head will congealimmediately after impact on the building platform due to cooling,Because of increased surface tension and viscosity in the solid state amelting of the release agent will be avoided. Thus, a three-dimensionalframe of the current object contour and the additional grid structurewill be generated. The height of this release agent frame above theexisting plane defines the slice height.

After completion of the release agent application the resin applicationstarts under computer control. This can be done in several ways, Onepossibility is to move a resin reservoir with a defined orifice acrossthe platform. Through the orifice a defined amount of resin will beapplied on the building platform.

Another solution concerns dispensing a certain amount of resin from areservoir at one edge of the platform across the entire buildingplatform by means of a blade analogous to silk-screen printing, or aroller.

Also possible is a dispensing of the resin by means of a silk-screen.The silk-screen will be positioned in a certain height above theplatform which represents the slice height. A predefined amount of resinwill be applied to the silk-screen and subsequently pressed through bymeans of a Rakel.

In all of these processes it is necessary to ensure a tight contactbetween release agent and resin. The height of the resin must be atleast corresponding to a slice height. After or during the applicationof the resin the resin will be hardened. This is possible by means of atemperature dependent phase change or a curing reaction of the resin,The curing reaction can e.g. be initiated by introducing a hardeningagent when applying the resin or by radiation introduced by means of anappropriate device.

In the next step the layer thickness is adjusted and excess material isremoved, e.g. by means of a sucking device. It is important to make surethat the surface of the release agent is bare after removing the excessmaterial, such that in the next step a direct contact between therelease agent layer introduced next and the already existing releaseagent structure can be realised. The adjusting of the layer thicknesscan be realised by means of an appropriate milling cutter or a movingcutting edge of an other type. By appropriately carrying out the step ofdepositing the resin the adjusting can be omitted completely or can becarried out only after a number of layers has been built in order tocontrol the work tolerance in the vertical direction. To permit that theadjusting steps can be omitted or the number of adjusting step can bereduced, it has to be avoided that resin material is deposited on therelease agent or flows due to surface tension effects.

In the following step the building platform is lowered by a distancecorresponding to the layer thickness and, the geometrical data of thecross section in the next cutting plane of the thin-walled shell aroundthe three-dimensional body is processed in the control computer. Theprocess is restarted beginning with the applying of the release agent.

The above described process is repeated until the last layer iscompleted. Then the complete material block filling the building volumeis taken off the building device and those parts of the resin which donot belong to the three-dimensional body and which have served as asupport for the three-dimensional body are separated along the borderingrelease agent. Then the three-dimensional body can be cleared from restsof the release agent. The clearing can be carried out by means of asolvent, preferably by means of water, moreover, cavities filled up withrelease agent can be cleared through bores which already existed orwhich are manufactured for this purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is explained referring to the encloseddrawing.

In the drawing:

FIGS. 1a-1 f show perspective views of the steps of the process,

FIG. 2 shows a plan view of a slice of the three-dimensional body havinga closed cavity from which material not belonging to the body cannot beremoved,

FIG. 3 shows a process chart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a shows the movement for lowering the building platform 1 withinthe building box 2 of the building device by a distance corresponding tothe layer thickness.

Then, FIG. 1b shows the applying of a release agent 3 by a single-dropgenerator 4 onto selected areas, wherein a pattern according to thecross-section in the respective height level of a thin-walled shell 5around the three-dimensional body 6 is generated. Moreover, furtherrelease patterns 5 are deposited extending to the walls of the buildingbox 2.

FIG. 1c shows the filling of the layer within the building box 2 with acurable resin 7 by means of the dosing device 8.

Then, as shown in FIG. 1d, the layer thickness is adjusted by a removingprocess carried out by means of a rotating cutter 9, such that therelease patterns 5 are cleared and get a bare surface again.

FIG. 1e shows the next lowering of the building platform 1.

The processes shown in FIGS 1 b to 1e are repeated as often as requireduntil the complete three-dimensional body 6 is formed of thin layers ofthe resin material 7. Then, the three-dimensional body embedded infurther parts consisting of resin material is completely taken off thebuilding box 2 and is separated from the further parts.

FIG. 1f shows the separating of the three-dimensional body 6 by means ofremoving the parts exterior of the bordering release patterns 5.

FIG. 2 shows the plan view on a cross section of the three-dimensionalbody 6, which cross section is given as an example and shows a core 10which cannot be removed. In order to clear the cavity from the coreafter terminating the process the core is made of the release agent 3.After termination of the process the release agent 3 is dissolved inthis area and is removed through an opening 11. The release patterns 5can be clearly seen, which serve as aids for separating thethree-dimensional body 6 from other parts after the termination of theprocess. Due to the release patterns even three-dimensional bodies 6comprising an undercut can be separated from the other parts.

FIG. 3 schematically shows the sequence of the data flow of the process.First, the data of the thin-walled shell 13 around the three-dimensionalbody are calculated from the CAD-data 12. For this purpose, in terms ofdata calculation, a thin-walled shell 13 is created covering the surfaceof the three-dimensional body, Further, in this step additional releasepatterns 5 are generated by checking for undercuts. Then, in thecalculation process, only the release patterns 5 are cut into thinslices according to the layer thickness. Layer data 14 is obtained,which can be passed to the control device 15. This control device 15controls the movement of the single-drop generator 4 over the buildingplatform 1 according to the layer data 14, such that the releasepatterns are built. This is realised by means of the xy-control unit 16of the single-drop generators 4. Then again, a filling step 17 of theresin material by means of the dosing device 8 is carried out. This stepis followed by a hardening 18 of the resin.

Then, in step 19, the control device 15 adjusts the layer thickness bymeans of a tool 9. Then the building platform 1 is lowered in step 20.Then, in the control device 15 an enquiry 21 follows checking whetherthe three-dimensional body is completed, that is, whether all layer data14 has been processed. If this is not the case, the control device 15goes to the controlling of the single-drop generator 4, in order tostart with the new layer. The process is repeated up to the enquiry 21.If by this enquiry 21 is found out, that the three-dimensional body 6 iscompleted, the process is terminated. Now, the three-dimensional body 6can be taken off the building box 2 in step 22 and can be separated fromother parts by removing the supporting parts along the release patterns5 in step 23.

This separating from other parts can be simplified, if a watercontaining release agent is used for generating the release pattern 5.The whole three-dimensional body 6 can then be heated after taking itoff the building box 2, e.g. by means of a micro wave furnace, such thatthe water abruptly evaporates and the thereby generated forces pushapart the supporting parts from the three-dimensional body along therelease patterns.

If not only one three-dimensional body is to be generated, since e.g. asmall series of bodies is required, it is possible to use the supportingparts for producing a forming tool.

What is claimed is:
 1. Method for producing a three-dimensional body,wherein the production of the three-dimensional body is carried outlayer-wise, the method comprising: selectively depositing two differentmaterials in each layer to follow an exterior contour of thethree-dimensional body in said layer, a first material of the differentmaterials being a release material and a second material of thedifferent materials being a building material for building-up thethree-dimensional body, wherein, at first, the release material isselectively deposited in a shape of a line to form a thin-walled shellaround the exterior contour of said three-dimensional body in therespective layer, whereafter the building material is deposited to fillremaining areas surrounded by the shell.
 2. Method according to claim 1,wherein the three-dimensional body and a support body are produced in alayer-wise manner by depositing said building material inside andoutside the thin-walled shell in each layer whereby a release jointbetween said three-dimensional body and said support body is generatedby said thin-walled shell.
 3. Method according to claim 1, wherein forgenerating closed or undercut cavities in the three-dimensional body,said release material is selectively deposited within the shell in eachrespective layer in a layer-wise manner to fill regions belonging to thecavity volume.
 4. Method according to claim 1, wherein a wax material isused as said release material.
 5. Method according to claim 1, wherein acast resin is used as said building material.
 6. Method according toclaim 5, wherein deposition of the building material is carried out byflooding and subsequent removing of excess material.
 7. Method accordingto claim 1, wherein a powder material is used as said building material.8. Method according to claim 7, depositing said building material iscarried out by spreading and stripping the building material.
 9. Methodaccording to claim 1, wherein the layer deposited last is evened andsmoothed in connection with loosening material and the loosened materialis removed.
 10. Method according to claim 1, wherein said releasematerial is deposited by means of a drop-on-demand printing head. 11.Method according to claim 1, wherein said building material comprisestwo components, each of which not hardening separately from the other,wherein said components are mixed before depositing the buildingmaterial and the building material formed by the mixed components ishardened after the deposition of the building material.
 12. Methodaccording to claim 1, wherein said building material is hardened bywhole-plane irradiation.
 13. Method according to claim 1, wherein saidthree-dimensional body is built-up in a building box on a buildingplatform and said building material is hardened by heat conductionthrough said building platform and said building box.
 14. Methodaccording to claim 1, wherein said building material is hardened bysintering.
 15. Method according to claim 1, wherein said buildingmaterial is hardened by applying gas.
 16. Method according to claim 2,wherein the release material is deposited in each layer to additionallyform a grid structure of release material outside the thin-walled shell,and the building material is deposited inside and outside the shell tofill remaining areas inside the thin-walled shell and between the gridstructure.
 17. Method for producing a three-dimensional body, whereinthe three-dimensional body is divided into layers and producedlayer-by-layer, the method comprising the following sequential steps forbuilding each said layer: depositing a first material to form aline-shaped shell defining a boundary of the three-dimensional body insaid layer; depositing a second material different from the firstmaterial, wherein the second material deposited in an area surrounded bythe line-shaped shell is for building-up the three-dimensional body insaid layer and the second material deposited outside the area surroundedby the line-shaped shell forms supporting material.